The present invention relates in general to a recording apparatus for writing or inscribing representations on a surface with pens or similar writing means. More particularly, the invention is concerned with improvements in a recording apparatus used as a peripheral output device for a computer, business machines or other instruments and having an indexable multi-station pen-holding head which holds plural pens of different colors, types, etc., and which is capable of changing the pens from one to another through movements of a carriage of the apparatus.
As a peripheral output device for computers and other data processing equipment, there are presently available various writing or plotting instruments so-called "pen-plotters" such as those called "X-Y plotters" and "graphic printers, which effect a recording with a pen or pens on a suitable recordng medium to write or inscribe characters (letters, numbers, symbols, etc. to form words, statements, etc.) or to plot or draw figures, drawings, illustrations or any graphical representations desired. In recent years, an increasing demand for color display has been met with a wide spread of multi-color pen-plotters, which use plural or multiple color pens that are automatically selectable. For such multi-color pen-plotters, different types of pen changing mechanisms or systems are proposed. For example, multiple color pens are stored in a storage station which is located near a predetermined recording area of a plotting apparatus, and a selected one of the color pens is held by a pen holder which is movable along X and Y axes as desired. In this system, the pen holder is returned to the storage station each time the color pen is changed from one to another. After a new color pen is installed in the pen holder at the storage station, the pen holder then goes to an original position to resume or continue a writing, plotting or any other desired recording operation. This type of system is complicated in its mechanism for interchanging the color pens. Such complicated pen changing device or mechanism is not applicable or structurally adaptable to a small-sized printer which uses a rotatable platen for holding and feeding a sheet of paper, i.e., recording medium.
There is also known a multi-color (multi-pen) recording apparatus wherein a recording sheet is fed along an X axis through rotation of a platen, while a selected pen is moved along a Y axis through movement of a carriage along the platen. An example of such a recording apparatus is shown in Japanese Patent Application laid open in 1982 under Publication No. 57-89966, wherein a carriage rotatably supports an indexable drum which holds multiple color pens such that their axes are spaced from each other circumferentially of the drum. The indexable drum is provided with a ratchet wheel fixed to the drum body, while a stationary pawl is disposed at one end of the carriage travel. When the carriage is moved close to the stationary pawl, a tooth of the ratchet wheel of the indexable drum comes into engagement with the stationary pawl, whereby the drum is rotated through a predetermined angle corresponding to an angular spacing of the ratchet teeth. In this arrangement, the angular increment of the indexable drum per engagement of the pawl with the ratchet tooth (per reciprocation of the carriage) is limited. Hence, where a comparatively small number of color pens are disposed on the drum, for example, when the drum is adapted to receive four color pens, a single reciprocation of the carriage (i.e., a single engaging action of the pawl with a tooth of the ratchet wheel) is not sufficient to rotate the drum from one station to the next. That is, the carriage must be reciprocated several times to bring the color pen on the next station into position (to change the color of a pen used on the apparatus). Thus, a pen changing device of the above known apparatus requires time-consuming repeated reciprocations of the carriage, and is relatively complicated in mechanism.